Solvent welding polybutene-1

ABSTRACT

A process for solvent welding pure polybutene-1, or blends or copolymer of polytbutene-1 to polybutene-1 where the polybutene-1 items are contacted with a solvent such as methylene chloride, tetrahydrofuran or cyclohexane and then contacted together within a variable period of time after solidification of the polybutene-1 items.

This is a continuation of application Ser. No. 679,426, filed Dec. 7,1984 now abandoned.

The present invention pertains to a process for solvent weldingpolybutylene. More particularly, the present invention pertains to aprocess for solvent welding polybutene-1 wherein the polybutene-1 itemsto be welded are solvent welded within a certain time interval afterpolybutene-1 solidification from a melt.

BACKGROUND OF THE INVENTION

Polybutene-1 is widely used for production of flexible pipe, pipefittings and various injection molded articles. Flexible pipe isgenerally manufactured by extrusion. However, difficulties arise injoining polybutene-1. Joining polybutylene articles has beenaccomplished by conventional mechanical means such as threaded jointsand flange connections, by thermal means such as flame or electricalresistance welding, or fusing with a welding sleeve, where externalpressure is applied to articles being joined at predetermined timesduring the welding process so that the articles in the welding sleeveare held in contact throughout the operation. See U.S. Pat. No.3,506,519.

Fusion welding is a commonly employed method of joining thermoplasticmaterials. Heat is applied or generated by any of a wide variety ofmethods at the two surfaces to be joined until they become molten. Thesurfaces are then brought together while they are still in the moltenstate, whereafter polymer chain segment interdiffusion proceeds and theinterface between the two original surfaces becomes diffuse oraltogether disappears. Subsequent cooling then restores the materialstrength and the bonded region may have strength equal to that of thesurrounding material. The strength of amorphous polymers develops uponvitrification or passing below the glass transition temperature ofentangled chains whereas that of semicrystalline polymers develops bythe crosslink-like network of crystalline domains. It is common practiceto join polybutylene by fusion welding.

Non-crystalline, amorphous polymers such as polystyrene or polycarbonatecan be readily solvent welded to form strong joints simply by theapplication of an appropriate solvent to the surface, followed by thebringing together of two such surfaces for a certain length of time.This process generally occurs without the application of heat, by slowsolvation of the amorphous polymer at the two surfaces which increasesthe chain segment mobility, effectively lowering the glass transitiontemperature locally to ambient temperature. Subsequently, chainentanglement across the interface can follow and diffusion of solventinto the surrounding material then gradually restores the polymer to itsoriginal properties. This process leaves the two surfaces effectivelywelded together with very high strength, often approaching the fullstrength of the material. This process is analogous to fusion weldingbut has the advantage that it can be accomplished more leisurely and atordinary temperatures.

In contrast to non-crystalline, amorphous polymers, however,semicrystalline polyolefins such as polypropylene, polyethylene andpolybutylene, generally cannot be successfully joined by solventwelding. In these materials the amorphous polymer segments areconstrained by participation in nearby crystallites. The response ofthis type of crystalline-amorphous structure to solvents is analogous tothat of a crosslinked network. Swelling of the amorphous phase by goodsolvents can occur, but unless the crystallites dissolve or are melted,the chain segments are not free to diffuse across the interface and toentangle into the adjacent surface. In the process of fusion welding, onthe other hand, the crystallites are not longer present and intersegmentdiffusion is facile. There has been a long felt need in thethermoplastic industry for a method of solvent welding semicrystallinepolymers.

U.S. Pat. No. 4,113,804 claims various polybutene-1 compositions thatcan be solvent welded and that can be used with solvent to formadhesives for those compositions. However, all of these compositionsmust contain EPDM interpolymer elastomer of ethylene, polyene andmonoolefin, an amorphous, non-crystalline ingredient. Column 3, line 50of U.S. Pat. No. 4,113,804 reveals that the amorphous elastomer ispresent in an amount which enhances the adhesive qualities of thepolybutene-1, indicating clearly its role in affecting weldability.Column 3, line 47 reveals that the amorphous elastomer may be present inamounts greater than the polybutene-1. Further, U.S. Pat. No. 4,113,804in column 12, line 10 discloses more rapid crystallization of theaforementioned blends than occurs with pure polybutene and claims thatas an advantage. Still further, U.S. Pat. No. 4,113,804 reveals incolumn 9, line 24 that, prior to welding, the plastic article may betreated with an oxidizing material but nowhere mentions the time windowimmediately after solidification from the melt as a necessary parameterof the invention. No examples are given showing the effectiveness ofsolvent welding of these amorphous EPDM compounds.

SUMMARY OF THE INVENTION

It is the essence of this invention to teach a hitherto unknown methodfor solvent welding crystalline polybutylene-1, crystallinepolybutylene-1 copolymers and crystalline polybutene-1 blends in whichit is the inherent retarded crystallization of polybutene-1 that isemployed to effect true solvent welding of the semicrystalline polymerphase without the addition of non-crystalline components. The instantinvention relies on carrying out solvent welding in a time window afterthe surfaces to be joined have been cooled from the melt. The methoddiffers from fusion welding in that the bonding takes place at ambienttemperatures rather than above the crystalline melting temperature.

The method recited by the instant invention for solvent weldingmaterials containing polybutene-1 crystallinity such ashomopolybutene-1, its copolymers and blends with other thermoplastics isas follows: (1) Freshly melt formed and solidified articles and/orarticles having surfaces that were freshly fused and resolidified areselected for welding. (2) The welding is carried out in a time windowprior to excessive, spontaneous crystallization of the polybutene-1phase but after solidification of the surfaces. For homopolybutene-1 andcyclohexane at normal ambient temperatures, the time window aftersolidification is approximately 15 minutes. (3) Solvent is applied tothe article surfaces. (4) The surfaces are brought into intimatecontact. (5) The surfaces are allowed to remain in contact forsufficient time for the solvent to diffuse away from the joint.

DRAWINGS

FIG. 1 is a laminate with a polybutene-1 cap layer on polypropylene.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a process for permanently adhering an item ofpolybutene-1 to a second item of polybutene-1. More specifically, it isa process for permanently adhering an item of either pure polybutene-1,a polybutene-1 copolymer or blends of same to a second item ofpolybutene-1. In the polybutene-1 copolymer, the butene-1 is thepredominant monomer, the other monomer being a monoolefin of C₂ to C₁₀.The blends may contain pure polybutene-1 or polybutene-1 copolymers withany polyolefin from C₂ to C₆, especially polyethylene and polypropylene.The polymer blend should contain sufficient polybutene-1 or polybutene-1copolymers so the polybutene items can be solvent welded. The polymer ofbutene i.e., polybutene-1, is a normally solid crystalline, isotactic,linear polymer having a molecular weight in excess of 100,000. Thepolymer is generally insoluble in diethylether and most other commonsolvents and soluble in orthodichlorobenzene. The polybutene-1 in thisinvention is isotactic polybutene.

Sections of pipe and sheets of film in the composition of this inventioncan be secured together using the solvents of this invention.Alternatively, for convenience of application and/or improved surfacecontact during joining, the solvent can be applied in the form of acement having higher viscosity than that of the pure solvent. Saidcement is formed by the dissolution in the solvent of minor amounts ofpolybutene-1 or a polybutene-1 copolymer which will then become anintegral part of the final joint. Polybutene-1 in the form of pellets,film, granulate or powder will dissolve in the solvents of thisinvention by the application to the mixture of heat and shear. Suchcements are convenient for use since they tend to remain metastablewithout crystallization, for extended time, even when ambient solubilityhas been exceeded in the composition. If crystallization does eventuallyoccur, changing the rheology of the cement and preventing participationof the dissolved polymer in the formation of the joint, the originalconsistency can be easily restored by briefly reheating the cement.Alternatively, an amount of polybutene-1 or PB-1 copolymer may be finelydivided and admixed with a sufficient amount of solvent or solventcement to provide a mixture of putty like consistency which may bedried. The putty is self-adhering to plastic articles made from thepolybutene-1, especially when they have been freshly solidified from themelt. The putty could also be molded into the shape of a pipe fitting.The molded fitting can be dried and then solvent welded to a pipe usingan adhesive of this invention.

First, polybutene-1 items or their surfaces are melted to liquificationand then cooled or allowed to cool to solidification. Then thesolidified polybutene-1 items are contacted with a sufficient amount ofthe solvent or solvent cement to allow polymer segments within thepolybutene-1 items to entangle upon contact of the items. The solventmay be selected from the group of methylene-chloride, tetrahydrofuran(THF), or cyclohexane, although any other solvent in which polybutene-1has a finite solubility may be used.

The polybutene-1 surfaces to be joined are contacted with an amount ofsolvent or cement sufficient to form a film between the surfaces whenthey are brought into contact, preferably a continuous film withoutbubbles or gaps. Some degree of surface roughness on one or both of thearticles to be joined may assist in the formation of solvent weldedjoints by trapping solvent between the surfaces when they are broughttogether under pressure.

The solvent is preferably cyclohexane which yields a solvent weldingtime window of approximately twenty (20) minutes. When the solvent iscyclohexane the solidified polybutene-1 items may be contacted with thesolvent and brought together as long as twenty (20) minutes after thepolybutene-1 solidification without loss of solvent weldability. Whenthe solvent is methylene-chloride or tetrahydrofuran, the contact wouldtake place within the first two minutes after solidification of thepolybutene-1 items from the liquid melt.

The polybutene-1 may be in the form of a cap layer on polypropylene asmay be seen in FIG. 1. Thus, a sheet or film laminate with apolybutene-1 cap could be solvent welded. This may be useful wherepolypropylene-type characteristics of the sheet or film are desired.

EXAMPLE 1

Lap joints of Shell grade 4127 polybutene-1 homopolymer were prepared byjoining two half tensile bars after their outermost surfaces had beenbriefly fused and then allowed to solidify in ambient air. Experimentsshowed that solidification occurred very quickly and that the surfacecooled to approximately room temperature within less than about oneminute. The elapsed time between removal of the fusion heat source andwelding was varied to determine the available solvent welding timewindow. A fusion welding control experiment, wherein no solvent wasemployed, was included. In other experiments, methylene chloride,tetrahydrofuran or cyclohexane containing 5% dissolved polybutene wereapplied to the surfaces at varying intervals after solidification, justprior to bringing the surfaces together.

After a period of five days the lap joints were stressed to failure. Ata stress level of about 600 psi of lap surface area, the tensile barsfailed cohesively, leaving the joint intact. When failure occurred atstress levels below 600 psi of lap area the joints separated. Theoutcome of these experiments is shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                      SOLVENT WELDING TIME                                            SOLVENT       WINDOW (MIN.)                                                   ______________________________________                                        None (Fusion) 0.6                                                             Methylenechloride                                                                           2                                                               Tetrahydrofuran                                                                             2                                                               5% PB/cyclohexane                                                                           15                                                              ______________________________________                                    

The results in Table 1 indicate that the use of methylene chloride orthe THF can allow solvent welding to be accomplished up to two minutesafter removal of the heat source, whereas the "open time" for fusionwelding is only 0.6 minutes, an increase in the time available forwelding of more than three (3) fold. When 5% PB/cyclohexane was used,the time was extended to 15 minutes, an increase of twenty-five (25)fold. Neat cyclohexane has been previously shown by applicants to beeffective but was not included in this particular time series.

Applicants speculate that this type of welding is possible because ofthe slow crystallization rate of polybutylene. It appears that weldingoccurs between two layers of swollen amorphous polybutylene by segmentinterdiffusion, followed by intercrystallization. The possibility forsolvent welding gradually decreases as crystallization advances in thesurfaces to be joined. Ordinary polybutene-1 samples that are nottreated in the manner of this invention are generally too highlycrystalline to be solvent welded.

The solvent welding time window may be extended beyond the fifteenminutes by use of a better solvent, a higher joint forming temperatureand/or methods for inhibiting the crystalline rate, such as holding thesolidified surfaces at a low temperature prior to solvent welding.

Variations of the ideas and method expressed in the above descriptionwill become apparent to one skilled in the art. It is therefore to beunderstood that within the scope of the claims the invention may bepracticed otherwise then as specifically described.

What is claimed is:
 1. A joined article prepared from first and secondarticles comprising a member of the group consisting of: polybutene-1homopolymer, a polybutene-1 copolymer or blends thereof, and joined by asolvent welding technique wherein said solvent welding techniqueconsists of the steps of:melting and cooling to solidification saidfirst and second articles; contacting at room temperature saidsolidified first and second articles with a solvent comprising a memberof the group consisting of methylene chloride, tetrahydrofuran, andcyclohexane; contacting said solvent contacted first article with saidsolvent contacted second article at room temperature to achieve asatisfactory bond.
 2. The joined article of claim 1, wherein said joinedarticle is prepared using a solvent in the form of a cement or anadhesive.
 3. The joined article of claim 1, wherein said joined articleis prepared by contacting said first and second articles together withintwenty minutes after melting and cooling said first and second articlesto solidification.
 4. The joined article of claim 1, wherein said joinedarticle is prepared by contacting said first and second articlestogether within twenty minutes after melting and cooling said first andsecond articles to solidification.
 5. The joined article of claim 1,wherein said joined article is prepared by contacting said first andsecond articles together within two minutes after melting and coolingsaid first and second articles to solidification.
 6. A joined pipeprepared from first and second pipes comprising a member of the groupconsisting of polybutene-1 homopolymer, polybutene-1 copolymer or blendsthereof, and joined by a solvent welding technique which consists of thesteps of:melting and cooling to solidification said first and secondpipes; contacting at room temperature said solidification first andsecond pipes with a solvent comprising a member of the group consistingof methylene chloride, tetrahydrofuran and cyclohexane; and contactingsaid solvent contacted first pipe with said solvent contacted secondpipe at room temperature to achieve a satisfactory bond.
 7. A processfor permanently adhering a first item of either pure polybutene-1, apolybutene-1 copolymer or blends of the same, to a second item ofpolybutene-1, which comprises the steps of:melting and cooling tosolidification, one or both of said first and second items ofpolybutene-1; contacting at room temperatures said solidifiedpolybutene-1 first and second items with an amount of a suitable solventsufficient to allow polymer segments within said first and secondpolybutene-1 items, upon contact of said first and second polybutene-1items, to entangle; and contacting at room temperature said firstsolvent contacted polybutene-1 item with said second solvent contactedpolybutene-1 item to achieve a satisfactory bond.
 8. The process ofclaim 7, wherein said solvent is selected from the group consisting ofmethylene chloride, tetrahydrofuran, and cyclohexane.
 9. The process ofclaim 7, wherein said solvent is in an adhesive or cement form.
 10. Theprocess of claim 7, wherein said contacting said first and secondsolidified polybutene-1 items takes place within twenty minutes afterpolybutene-1 solidification.
 11. A process for permanently adhering afirst item of either pure polybutene-1, a polybutene-1 copolymer orblends of the same to a second item of polybutene-1 which comprises thestep of:melting and cooling to solidification said first and seconditems of polybutene-1; contacting at room temperature said solidifiedpolybutene-1 first and second items with an amount of cyclohexanesufficient to allow polymer segments within said first and secondpolybutene-1 items, upon contact of said first and second polybutene-1items, to entangle, wherein said solidified polybutene-1 first andsecond items are contacted with said cyclohexane within twenty minutesafter polybutene-1 solidification; and contacting at room temperaturesaid first cyclohexane contacted polybutene-1 item with said secondcyclohexane contacted polybutene-1 item within twenty minutes to achievea satisfactory bond.
 12. The process of claim 11 wherein cyclohexane isin an adhesive or cement form.
 13. A process for permanently adhering afirst item of either pure polybutene-1, a polybutene-1 copolymer orblends of the same to a second item of polybutene-1, which comprises thesteps of:melting and cooling to solidification said first and seconditems of polybutene-1; contacting at room temperature said solidifiedpolybutene-1, first and second items with an amount of methylenechloride or tetrahydrofuran sufficient to allow polymer segments withinsaid first and second polybutene-1 items, upon contact of said first andsecond polybutene-1 items to entangle, wherein said solidifiedpolybutene-1 first and second items are contacted with said methylenechloride or said tetrahydrofuran within four minutes after polybutene-1solidification; and contacting at room temperature said first methylenechloride or tetrahydrofuran-contacted polybutene-1 item with said secondmethylene chloride or tetrahydrofuran-contacted polybutene-1 item withintwo minutes to achieve a satisfactory bond.
 14. The process of claim 13,wherein said methylene chloride or said tetrahydrofuran is in anadhesive or cement form.